Drafting devices are well known in the art. FIG. 2 and FIG. 3 show a typical prior art drafting apparatus, and the internal structure of a typical prior art top roller, respectively.
Referring to FIG. 2, a drafting apparatus D utilizing a four-point drafting system is comprised of four roller units: a front roller unit 1 (comprising front top roller 1a and front bottom roller 1b), a second roller unit 2 (comprising second top roller 2a provided with apron 2a', and second bottom roller 2b provided with apron 2b'), a third roller unit 3 (comprising third top roller 3a and third bottom roller 3b), and a back roller unit 4 (comprising back top roller 4a and back bottom roller 4b). Front top roller 1a, second top roller 2a, third top roller 3a, and back top roller 4a are all held by a bearing or the like arranged inside pivotable arm unit D'.
Downstream of the drafting apparatus D, the spinning frame also includes a spinning unit 5 that spins the drafted sliver into a yarn y using, for example, a vortex air current; and a nip roller 6a capable of freely contacting and separating from a delivery roller 6b that is continually rotated. The yarn y fed from the spinning unit 5 is nipped between the nip roller 6a and the delivery roller 6b, and fed downstream to a guide bar 7, a slack tube 8 and a yarn clearer 9 before being wound into a package 10 rotated by contact with a rotationally driven friction roller 11.
After being drawn from a sliver container 12, the sliver s is drafted by the drafting apparatus D, and spun into yarn y by the spinning unit 5. Next, the spun yarn y is nipped between the nip roller 6a and the delivery roller 6b, fed past the guide bar 7, the yarn clearer 9 and so on, and wound into the wound package 10 which is rotated in contact with the friction roller 11.
In reference to FIG. 3, the structure of the conventional prior art top roller T will now be explained. It should be noted that all the top rollers of the drafting apparatus D, including the front top roller 1a, second top roller 2a, third top roller 3a, and back top roller 4a, all share the structure shown in the drawing.
The top roller T includes a shaft 13 which is held by a bearing or the like mounted to the pivotable arm unit D'. The shaft 13 is comprised of three main sections: a bearing holding section 13a that supports an outside bearing 14a on the end of the bearing holding section 13a, and an inside bearing 14b at the base of the bearing holding section 13a, each bearing 14a, 14b having the same diameter and spaced a predetermined distance apart; a central section 13b having a diameter slightly larger than the bearing holding section 13a; and a base section 13c having a diameter slightly larger than the central section 13b. A washer 15 having a total diameter slightly larger than the inner diameter of the bearings 14a, 14b, is affixed to the end of the bearing holding section 13a with a bolt 16. The washer 15 prevents the bearings 14a, 14b from dislodging from the bearing holding section 13a.
A pressure applying spring 17, arranged between the two bearings 14a, 14b, simultaneously presses the outside bearing 14a against the washer 15, and presses the inside bearing 14b against the facing wall 13d formed at the juncture of the bearing holding section 13a and the central section 13a of the shaft 13. A tubular spacer 18 is formed around the periphery of the pressure applying spring 17, and arranged between the two bearings 14a, 14b. A roller tube 19 fixedly engages the bearings 14a, 14b, and encloses the central section 13b and bearing holding section 13a of the shaft 13, the bearings 14a, 14b, the pressure applying spring 17, and the spacer 18.
A C-ring 20 is arranged between a circular groove around the circumference of the spacer 18 and a matching circular groove formed on the inner surface of the roller tube 19, the C-ring 20 fixedly engaging the spacer 18 with the roller tube 19, and holding the spacer 18 and the roller tube 19 at a predetermined relative position. A cover 21 is fixedly inserted into the end of the roller tube 19, and an O-ring 22 is fixedly engaged to a circumferential groove cut into the surface of the central section 13b of the shaft 13 help prevent fibrous waste and other matter from entering the inner parts of the top roller T roller.
A top-cot 23 is attached around the circumference of the roller tube 19 and roughly envelopes the area occupied by the bearings 14a, 14b. The top-cot 23 makes contact with the sliver s that is drafted.
The bearing holding section 13a of this prior art shaft 13 of the top roller T supports the bearings 14a, 14b, and is formed to a uniform diameter generally between 6 mm and 8 mm. When the bearing holding section 13a has a small diameter (6 mm, for example), rigidity is sacrificed, and the bearing holding section 13a tends to warp under the heavy load generated by drafting the sliver. Another consequence of using the shaft 13 with a small diameter bearing holding section is that when the top roller T is attached or removed from the drafting apparatus D, large shocks such as might be caused by dropping the top roller T may also cause the shaft 13 to bend. Bends or warps in the shaft 13 lead to drafting abnormalities and flaws in the spun yarn y.
Rigidity of the shaft 13 can be improved when the bearing holding section 13a of the shaft 13 is larger (8 mm in diameter, for example), but when the bearing holding section 13a is larger, the balls 14a', 14b' in the bearings 14a, 14b must be made smaller, thereby reducing the durability and longevity of the bearings 14a, 14b.
In order to solve these problems of the conventional top roller of the drafting apparatus, it is an object of the present invention to provide a top roller that is light, rigid, and durable, and can be attached and removed without concern about damaging the shaft.